1. Field of the Invention
The present invention relates to a solid-state image pickup device and a method of making the same.
2. Description of the Related Art
Solid-state image pickup devices have recently been proposed which include an optical waveguide in order to increase the quantity of light incident on a photoelectric conversion unit.
Japanese Patent Laid-Open No. 2007-141873 discloses a solid-state image pickup device having a light-receiving area where pixels receiving light from a subject are arranged and a light-shielding area where light-shielded pixels are arranged. In the solid-state image pickup device illustrated in FIG. 1 disclosed in Japanese Patent Laid-Open No. 2007-141873, a first high refractive index region, serving as an optical waveguide, is disposed just above a first photoelectric conversion unit positioned in the light-receiving area. A second high refractive index region is disposed between a second photoelectric conversion unit positioned in the light-shielding area and a first interconnect disposed so as to cover the second photoelectric conversion unit.
The solid-state image pickup device disclosed in Japanese Patent Laid-Open No. 2007-141873 has the following disadvantages. First, the magnitude of dark current of each pixel in the light-receiving area may differ from that of each pixel in the light-shielding area. The reason is that the structure of the optical waveguide of each pixel in the light-receiving area markedly differs from that in the light-shielding area. Specifically, the upper surface of the first high refractive index region, serving as the optical waveguide of the pixel in the light-receiving area, differs from that of the second high refractive index region, serving as an optical waveguide of the pixel in the light-shielding region, in the level relative to a semiconductor substrate as illustrated in FIG. 1 of Japanese Patent Laid-Open No. 2007-141873. Accordingly, those regions differ from each other in the cross-sectional area.
Second, the parasitic capacitance of an interconnect for signal transmission of each pixel in the light-receiving area may differ from that of each pixel in the light-shielding area. The reason is that the structures of interconnects in the light-receiving area markedly differ from those in the light-shielding area. Specifically, the structure of a first interconnect closest to the semiconductor substrate in the light-receiving area differs from that in the light-shielding area.
Third, the extent of damage caused by a making process in the light-receiving area may differ from that in the light-shielding area. The reason is that a process of forming the optical waveguide of each pixel in the light-receiving area differs from that in the light-shielding area.
The above-described first to third disadvantages may increase the difference in noise between pixels in the light-receiving area and pixels in the light-shielding area.